System and method for restarting an engine

ABSTRACT

Various systems and methods are described for controlling an engine in a vehicle, the engine being coupled to a transmission. One example method comprises, under selected braking conditions, shutting-off the engine and spinning-down the engine to rest while the vehicle is traveling, and in response to a foot-off-brake event, restarting the engine by at least partially engaging the transmission to assist in spinning-up of the engine from rest while the vehicle is traveling.

TECHNICAL FIELD

The present description relates generally to an internal combustionengine coupled to a transmission in a motor vehicle.

BACKGROUND AND SUMMARY

Vehicle engines may be configured to shut-off during idle conditionswhen the vehicle comes to a stop while a brake is applied and restartedonce the brake is released (e.g., a stop/start system) in order toreduce fuel consumption. Fuel consumption may be further reduced byshutting down the engine during braking or by shutting down the enginewhen the operator is not braking and not requesting torque, before thevehicle has come to a stop.

One approach to shutdown and subsequently restart the engine while thevehicle is traveling is disclosed in U.S. Pat. No. 6,951,525. In thecited reference, the engine is restarted prior to a transition fromfree-wheel mode to engaged clutch travel mode by employing the fuelinjection system using a charge regulator and/or an electric motor. Inone embodiment the charge regulator reactivates the engine bysequentially activating a fuel injection system. In an alternativeembodiment, engine restart may be supported by an electric motor.However, sequentially activating a fuel injection system to restart anengine is of little use in starting an engine that is not rotatingbecause the injected charge may not be compressed so that it can becombusted and thereby restart the engine. And, starting an engine usinga starter can interrupt other electrical systems since a large currentmay be required to restart the engine.

The inventors herein have recognized the above problems and have devisedan approach to at least partially address them. Thus, a method forcontrolling an engine coupled to a transmission in a vehicle isdisclosed. The method comprises, under selected conditions, shutting-offthe engine and spinning-down the engine to rest while the vehicle istraveling, and, in response to an operating condition, restarting theengine by at least partially engaging the transmission to assist inspinning-up of the engine from rest while the vehicle is traveling.

Specifically, in one example embodiment when the vehicle is moving, atorque converter or another clutch is engaged when an engine restart isrequested. Engaging the clutch transfers wheel torque to the at-restengine so that the engine is rotated. An electric pump may be drivenwhile the engine is at rest so that hydraulic pressure in thetransmission is maintained during engine rest conditions. Thetransmission clutches can be shifted based on vehicle speed so that adesired amount of starting torque can be applied to start the engine(e.g., top gear reduces the resulting vehicle deceleration rate during a“push start”). In this manner, vehicle inertia can be used to assist inspinning-up the engine from rest when the vehicle is moving. Thus, fuelcan be conserved by stopping the engine while engine torque is notrequired. And, the engine can be quickly restarted without having toengage the starter and draw current from the vehicle battery.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a vehicle illustrating variouspowertrain components.

FIG. 2 shows schematic diagram of an engine.

FIG. 3 shows a flow chart illustrating a control routine for an engine.

FIG. 4 shows a flow chart illustrating a control routine for an engineduring deceleration fuel shut-off.

FIG. 5 shows a flow chart illustrating a control routine for shuttingdown an engine.

FIG. 6 shows a flow chart illustrating a control routine for restartingan engine.

DETAILED DESCRIPTION

The following description relates to a method for controlling aninternal combustion engine coupled to a transmission in a motor vehicle.During selected conditions, including braking conditions in one example,an engine may be turned off and allowed to spin-down to rest while thevehicle is traveling. In one particular example, braking conditionsinclude when a vehicle speed and/or an engine speed are below respectivethreshold values and coasting or engine stop conditions may includefoot-off accelerator pedal conditions. As will be described below, insome embodiments, the transmission may be engaged and its gears able toshift while the engine is shutdown. In such a configuration, thetransmission may be shifted before the engine is restarted based on thespeed of the vehicle. As a result, the transmission may supply power tothe engine, by way of the vehicle wheels, and assist in enginerestarting. The transmission may provide torque to spinning-up theengine from rest in response to a condition, such as a foot-off-brakeevent. Thus, the engine can be restarted, at least under someconditions, using energy supplied from the moving vehicle.

Referring to FIG. 1, internal combustion engine 10, further describedherein with particular reference to FIG. 2, is shown coupled to torqueconverter 11 via crankshaft 40. Torque converter 11 is also coupled totransmission 15 via turbine shaft 17. Torque converter 11 has a bypassclutch (not shown) which can be engaged, disengaged, or partiallyengaged. When the clutch is either disengaged or being disengaged, thetorque converter is said to be in an unlocked state. Turbine shaft 17 isalso known as transmission input shaft. In one embodiment, transmission15 comprises an electronically controlled transmission with a pluralityof selectable discrete gear ratios. Transmission 15 may also comprisesvarious other gears, such as, for example, a final drive ratio (notshown). Alternatively, transmission 15 may be a continuously variabletransmission (CVT).

Transmission 15 may further be coupled to tire 19 via axle 21. Tire 19interfaces the vehicle (not shown) to the road 23. Note that in oneexample embodiment, this powertrain is coupled in a passenger vehiclethat travels on the road. While various vehicle configurations may beused, in one example, the engine is the sole motive power source, andthus the vehicle is not a hybrid-electric, hybrid-plug-in, etc. In otherembodiments, the method may be incorporated into a hybrid vehicle.

FIG. 2 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. Engine 10 may be controlled at least partially by a controlsystem including controller 12 and by input from a vehicle operator 132via an input device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber 30 of engine10 may include cylinder walls 32 with piston 36 positioned therein.Piston 36 may be coupled to crankshaft 40 so that reciprocating motionof the piston is translated into rotational motion of the crankshaft.Crankshaft 40 may be coupled to at least one drive wheel of a vehiclevia an intermediate transmission system. Further, a starter motor may becoupled to crankshaft 40 via a flywheel to enable a starting operationof engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.Exhaust camshaft 53 operates exhaust valve 54 in accordance with theprofile of a cam located along the length of the exhaust camshaft.Intake camshaft 51 operates intake valve 52 in accordance with theprofile of a cam located along the length of the camshaft. Exhaust camposition sensor 57 and intake cam position sensor 55 relay respectivecamshaft positions to controller 12. Pump 72 supplies oil to indexintake camshaft 51 and exhaust camshaft 53 relative to crankshaft 40based on commands to camshaft actuators (not shown) supplied bycontroller 12. Pump 72 may be electrically driven so that camshafts maybe indexed when engine 10 is not rotating.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someembodiments, combustion chamber 30 may alternatively or additionallyinclude a fuel injector arranged in intake passage 44 in a configurationthat provides what is known as port injection of fuel into the intakeport upstream of combustion chamber 30.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP. Intake passage 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, during operationof engine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; vehicle brake121; a profile ignition pickup signal (PIP) from Hall effect sensor 118(or other type) coupled to crankshaft 40; throttle position (TP) from athrottle position sensor; and absolute manifold pressure signal, MAP,from sensor 122. Engine speed signal, RPM, may be generated bycontroller 12 from signal PIP. Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold. Note that various combinations ofthe above sensors may be used, such as a MAF sensor without a MAPsensor, or vice versa. In one example, sensor 118, which is also used asan engine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by processor 102 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

Controller 12 also receives signals from and provides control signals toa transmission (not shown). Transmission signals may include but are notlimited to transmission input and output speeds, signals for regulatingtransmission line pressure (e.g., fluid pressure supplied totransmission clutches), and signals for controlling pressure supplied toclutches for actuating transmission gears.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Control routines for engine 10 are illustrated in the flow charts ofFIGS. 3-6. The flow chart in FIG. 3 depicts a routine for controlling anengine during various braking conditions. Depending on the brakingconditions, the routine of FIG. 3 leads to the control routine of FIG. 4or 5 in which the engine enters DFSO or the engine is shutdown,respectively. Finally, a routine for restarting the engine is displayedin FIG. 6.

Referring now to FIG. 3, the flow chart shows a control routine 300 foran engine, such as engine 10 in FIG. 2. Specifically, routine 300determines conditions for which it is desirable to deactivate combustionin the engine during operation by a driver. In one example, under someconditions a fuel supply to the engine may be shut-off (with the enginecontinuing to rotate), while under other conditions the engine may beshutdown to substantially zero rotation (e.g., via discontinuing ofspark, fuel supply, etc.). The routine allows the engine to restart whenthe driver demands torque or in response to other operating conditions.

At 310 of routine 300 in FIG. 3, it is determined if the engine shouldbe stopped. In one example, if the brake is applied (e.g., if a driver'sfoot is depressing the brake pedal) the routine proceeds to 312. If thebrake is not applied, or if the vehicle is not in an extended coastcondition, routine 300 moves to 322 where the routine determines ifengine combustion has been maintained. In another example, or inaddition to utilizing the brake signal, the change in vehicle speed overa time or a change in vehicle speed over a vehicle distance traveledinterval may be used to determine whether or not to deactivatecombustion in the engine. A change in vehicle speed and lack of a driverdemand torque may be used to indicate an extended vehicle coast periodor an extended vehicle decent from altitude. Further, the driver torquedemand can be used as an input to determine whether or not to deactivatecombustion in the engine. Thus, each of the previously mentionedconditions and other conditions may be used to determine when toshut-down the engine.

At 312, the routine determines whether entry conditions are met. Entryconditions may include, but are not limited to, engine purgingconditions, a charge state of a vehicle battery, engine temperature,emission control device temperature, etc. For example, the battery maybe employed to run various components (e.g., electric motors, lights,etc.) while the engine is off; thus, the engine may not be shutdownunless the battery attains certain amount of charge.

If the appropriate entry conditions are met, routine 300 continues to314 where it is determined if the vehicle speed (VS) is below a firstthreshold value. In the case in which it is determined that the vehiclespeed is greater than the first threshold value, routine 300 moves to320 where a deceleration fuel shut-off (DFSO) routine is initiated and afuel supply to the engine is shut-off but the engine continues torotate. The DFSO routine will be described in greater detail below withreference to FIG. 4.

Continuing with FIG. 3, if it is determined that the vehicle speed isless than the first threshold value, routine 300 proceeds to 316 whereit is determined if the difference between the current engine speed andidle speed (Δ=engine speed-idle speed) is less than a threshold amount.If the difference between the current engine speed and idle speed isgreater than the threshold amount, routine 300 moves to 320 where theDFSO routine is initiated. In contrast, if Δ (engine speed-idle speed)is less than the threshold amount, routine 300 continues to 318 where anengine shutdown routine is initiated, which will be described in detailbelow with reference to FIG. 5. Thus, one example, in response to afirst braking condition (e.g., Δ<threshold), the routine shuts off afuel supply to the engine while the engine continues to rotate, whereasin response to a second, different braking condition (e.g., Δ>threshold;the routine shuts-off the engine and the engine spins-down to rest.

In some embodiments, a single braking event may include both DFSO andshutting down the engine to rest, with the engine shut-down to restoccurring after operation in DFSO conditions. As an example, when thedriver begins braking, the vehicle may be traveling at 70 mph and thedifference between the engine speed and idle speed may be too high toshutdown the engine if a smooth restart is desired. As such, the fuelsupply to the engine may be shut-off while the vehicle decelerates, withthe engine continuing to rotate (e.g., during a first brakingcondition). During the same brake event (e.g., at a later time of thesame operator brake event), the vehicle may slow to a speed of 40 mph(due to the extended braking by the operator) and the difference betweenthe engine speed and idle speed may fall below the threshold amountallowing the engine to be turned off while the vehicle is traveling(e.g., during a second braking condition). As such, the engine istransitioned from continued rotation without fuel and spark, to ashut-down, engine rested, condition. The engine may be transitioned to asubstantially zero rotation state by disengaging a transmission gear,for example, and/or placing the transmission into neutral. Thus, theengine can be decoupled from the transmission output, thereby reducingthe torque supplied by the wheels to the engine through thetransmission. Alternatively, the transmission may still be in gear, orshifted to a different gear, while a forward clutch is disabled tode-couple the transmission output from the engine. Such operation isdescribed further with regard to FIGS. 4-5.

If, however, the vehicle speed and/or the Δ engine speed-idle speed donot fall below their respective threshold values, the routine may onlyemploy DFSO operation during particular conditions.

In another embodiment, the vehicle speed and the difference between thecurrent engine speed and idle speed may be below their respectivethreshold values and the routine may include only engine stoppedoperation during a particular engine deactivation sequence.

At 322, the routine determines if the engine is shut-down from aprevious execution of the engine shutdown routine (FIG. 5) or from aprevious execution of the DFSO routine (FIG.4). If so, routine 300proceeds to 324 and the engine restart routine is executed (FIG. 6),otherwise the routine maintains engine operation at 326.

Thus, routine 300 demonstrates how the engine will be controlled inresponse to various conditions while the vehicle is traveling. Dependingon conditions such as vehicle speed and engine speed, routine 300 maytransition to the routines of FIG. 4 and/or FIG. 5.

Turning now to FIG. 4, the flow chart in FIG. 4 depicts a controlroutine 400 for an engine during deceleration fuel shut-off (DFSO).Specifically, routine 400 determines conditions such as whether anoperator is pressing a brake pedal, whether an automatic cruise controlsystem is causing braking operation, and further including engine speedand vehicle speed once DFSO has begun. In response to the variousconditions, the engine may be shutdown or DFSO may be maintained untilfuel injection is resumed.

At 410 of routine 400, DFSO begins. Upon initiation of DFSO, fuelinjection is cut-off to the cylinders. The engine continues to rotate,due to transmission of torque from the vehicle's wheel(s) to the enginethrough an engaged gear of the transmission, for example.

Once DFSO has begun, it is determined if the vehicle speed is less thana second threshold value at 412 of routine 400. If it is determined thatthe vehicle speed is less than the second threshold value, routine 400proceeds to 414 where it is determined if the difference between thecurrent engine speed and idle speed is less than a threshold amount. Ifthe Δ engine speed-idle speed is less than the threshold amount, routine400 continues to 416 where routine 400 transitions to the engineshutdown routine of FIG. 5. As described above in one example, during asingle brake event, the engine shut-down operation may follow operationin DFSO when the vehicle speed and the Δ (engine speed-idle speed)decrease below respective threshold values. The transition may includechanging a gear of the transmission to a neutral, and/or disengaging atransmission gear to reduce torque from the wheel delivered to theengine, thus reducing engine speed to rest.

On the other hand, if at 412 it is determined that the vehicle speed isgreater than the second threshold value, routine 400 moves to 418 whereit is determined if the driver's foot is off the brake and/or if thethrottle position is greater than zero. Likewise, if it is determinedthat Δ (engine speed-idle speed) is not less than a threshold amount at414, routine 400 moves to 418. In such a condition, only the DFSOoperation may be performed in the single braking event.

In one example if it is determined that the driver's foot has releasedthe brake and/or if the throttle position is greater than zero, routine400 moves to 420 where fuel injection in one or more cylinders isresumed. If, instead, it is determined that the driver's foot is stillon the brake and/or if the throttle position is zero, routine 400proceeds to 422 where it is determined if there are other requests toinject fuel. For example, the temperature of an emission control devicemay need to be increased, and, in order to do so, the temperature of theexhaust gas may need to be increased. Thus, fuel injection may beresumed so as to increase the exhaust gas temperature, and in turn, theemission control device temperature. As another example, engine speedmay fall below a minimum engine speed threshold, thereby generating arequest to restart combustion in the already rotating engine. Otherconditions such as vehicle speed below a predetermined amount may besubstituted or added to the logic described above so that the DFSO logicproceeds to 418 and fuel injection is resumed, if desired.

Once it is determined there are no other requests to inject fuel,routine 400 proceeds to 422 where deceleration fuel shut-off ismaintained and the routine ends, but may be subsequently re-executed.

In this manner, routine 400 controls engine operation in response tovarious conditions during deceleration fuel shut-off. In someembodiments, the routine maintains DFSO until fuel injection isrequested or the brake is released. If the vehicle speed or thedifference between the current engine speed and idle speed fall belowtheir respective threshold values, routine 400 may transition to theroutine of FIG. 5, even during a single braking event.

As illustrated, the routines of FIGS. 3-4 control both DFSO and engineshut-down operation, as well as transitions from DFSO to engineshut-down operation, during vehicle braking operation. In this way, itis possible to achieve rapid response to driver demands, while reducingoxygen flow through the catalyst system when possible.

Referring now to FIG. 5, the flow chart illustrates a control routine500 for shutting-down the engine in response to a condition such as abraking event or extended vehicle coast (e.g., a moving vehicle andsubstantially no operator torque demand). Specifically, routine 500determines conditions for shutting down the engine and bringing enginespeed down to rest, and controls the engine, transmission, and torqueconverter lock-up accordingly.

In one example, when the engine is operating in a DFSO mode and it isdetermined to shut-down the engine and bring the engine to rest, theroutine first operates the transmission and/or torque converter tode-couple the engine from the driving torque of the wheels. For example,the transmission may have its forward clutch disengaged to maintain thetransmission in gear, but decoupled the engine from the wheels to enablethe engine to spin down to rest. In another example, the transmissionmay be shifted into neutral or a gear with an over-running clutch tode-couple the engine from the driving torque of the wheels and bring theengine to rest while the vehicle is still traveling. After the engineand transmission are decoupled, the engine goes to rest.

Alternatively, the engine may be shut-down from a combusting condition.Again, adjustment of the transmission may be used to bring the engine torest by shifting gear, adjustment of the forward clutch, etc., as notedimmediately above.

Additionally, the routine of FIG. 5 may further include adjustments tothe transmission to configure the transmission to improve enginerestarts. In the example where the transmission may be shifted duringengine rest (e.g., via hydraulic pressure generated by an electricallydriven pump), the gear of the transmission may be adjusted as thevehicle speed gradually reduces, so that as soon as an engine re-startrequest is issued, the transmission is in a desired gear to enabletorque to be transferred from the wheels, through the transmission, thusat least partially push-starting the engine. In this example, thetransmission may be transitioned to neutral (or a forward clutchdisengaged) to spin the engine down to rest, and then shifted to fourthgear (with the forward clutch disengaged), for example, while vehiclespeed is reduced from a first value to a second value, and then thetransmission may be shifted to third gear (while the forward clutch isdisengaged), for example, while vehicle speed is further reduced fromthe second value to a third value—all while the engine is shut down atrest and a braking condition is present. Then, in response to a releaseof the brake pedal, vehicle speed falling below a predetermined level,or another condition while in the third gear, the forward clutch can beengaged while initiating spark and fuel in the engine to restart theengine at least partially using the vehicle inertial. Further, duringsome conditions the starter may be engaged to assist the transmission tostart the engine.

Note that a gear may be selected during the engine off period based onthe available torque the gear would transfer from the tire back throughto the engine. A transmission clutch or the torque converter clutch maybe used to slip the gear such that all the torque available from thetire is not transferred to the motor. Slipping a transmission clutch ortorque converter during engine run-up can reduce torque disturbancesnoticeable to the operator.

Note that restarting torque disturbances may be reduced by selecting ahigher gear, quickly engaging a transmission clutch to rotate the engineabove 200 RPM, de-clutching the transmission into neutral as the engineaccelerates under its own torque provided by combustion, accelerate theengine to a speed synchronous with the transmission in a particulargear, and then re-engaging a transmission clutch. Thus, a smoother startmay be accomplished by selecting a gear that is higher than the gearthat would be selected by the transmission during similar drivingconditions. Further, as an alternate embodiment, a mechanical one-wayclutch may be used to link the transmission and the engine such that theengine may over run the transmission under some conditions. Themechanical clutch may be place in a configuration parallel with theengine torque converter if desired.

If the transmission is not shifted during engine rest conditions, thenduring or before the engine shut-down the transmission may be shifted toa desired gear for restarting. In this example, when transition fromDFSO or combustion to an engine rest condition, the forward clutch maybe disabled to de-couple the engine from the wheels (thus allowing theengine to spin down to rest), while at the same time the transmission isshifted to a desired gear (e.g., a high gear, such as a maximum gear) toenable improved engine restarting. Then, in response to a release of thebrake, vehicle speed falling below a predetermined level, or anothercondition, the forward clutch may be engaged to utilize vehicle inertialto at least partially spin up the engine, along with commencement offuel injection and spark to restart the engine.

At 510 of routine 500, it is determined if the engine is on, e.g.,carrying out combustion, such as conditions in which air and/or fuel areinjected to one or more cylinders of the engine and the engine isrotating. If it is determined that the engine is on at 510, routine 500proceeds to 512 where it is determined if push assist restart isenabled. During push assist restart operation, the transmission may beutilized to at least partially assist in spinning-up the engine fromrest while the vehicle is traveling during a subsequent restartcondition (e.g., a foot-off-brake event), where this engine startingoperation follows from conditions where the engine is shutdown due toconditions as described above.

If it is determined that push assist restart is enabled, routine 500continues to 514 where it is determined if shifting during engine restis enabled. Once it is determined that shifting during engine rest isenabled, routine 500 proceeds to 516 where a transmission and torqueconverter shifting control is executed.

In one example at 516, the transmission shifting and torque converterlock-up control can be carried out while the engine is off, suchoperation may be carried out to set the transmission and torqueconverter into a desired state for engine starting based upon theconditions of the engine start. For example, before the engine isshutdown, the transmission may be shifted to neutral, and while theengine is off the torque converter may be locked-up (e.g., engaged). Assuch, while the vehicle is traveling with the engine off, thetransmission may shift into an appropriate gear with the forward clutchdisengaged. Shifting the transmission while the engine is stopped allowsfor restarting the engine using a gear that will transmit sufficienttorque from the vehicle wheels to at least assist engine starting.Further, the gear may be selected in response to vehicle speed and adesired amount of torque that is to be transferred from the vehiclewheels to the engine.

As one example, the transmission may be shifted from neutral to a highgear in order to “push start” the engine via the high gear andengagement of the forward clutch while reducing a torque dip that may befelt by the operator. In some embodiments, the push start may bepre-programmed to be executed by the controller during specific brakingevents, when vehicle speed is above a threshold, or during otherconditions such as change in vehicle speed less than or greater than athreshold. In other embodiments, push start may be programmed to beexecuted during and in response to selected braking events, but notothers.

At 516 routine 500 controls the transmission fluid pressure as well asthe transmission clutches and the torque converter clutch. In oneembodiment, the transmission fluid is pumped by an electrically drivenpump when the engine is not rotating. The transmission fluid pumppressure can be controlled by controller 12, described in FIG. 2. Theoutput of the electrically driven oil pump can be adjusted in responseto ambient conditions (e.g., air temperature, air pressure, and thelike) and in response to engine conditions (e.g., oil temperature). Inone example, the line pressure supplied to clutches in the transmissioncan be controlled during engine stop by sending a command current ormodulated voltage signal to a pressure regulating valve located withinthe transmission. Similarly, transmission clutches can be engaged ordisengaged by a command current or modulated voltage signal sent to thetransmission clutches. Further, clutch slippage can be controlled bymonitoring the transmission input and output shaft speeds and thenadjusting the demand current or duty cycle applied to valves thatregulate the transmission fluid pressure that is applied to theclutches. The torque converter clutch may also be controlled bysupplying the clutch actuator a command current or modulated voltage.Note that the torque converter clutch may be an application specificdesign that is used to restart the engine from rest. If so, separatecontrol for two torque converter clutches may be provided.

From the transmission and torque converter shifting control, the routinecontinues to 518 to shut-down the engine. Herein, shutting down theengine includes shutting-off the engine and spinning-down the engine torest, e.g., by de-coupling the engine from the transmissionoutput/wheels and/or stopping fuel injection/spark. As described above,depending on conditions, the engine may be shutdown to rest while thevehicle is traveling. In one example, the engine intake and exhaust camsare indexed to a position that reduces air flow through the cylinderswhile the engine is at rest. The intake and/or exhaust cams may beindexed when the engine is spinning-down or when the engine is at rest.By adjusting the camshafts to positions that reduce flow, convectiveflow through the engine and exhaust system can be reduced therebylimiting oxygen flow through the engine while the engine is at rest.Similarly, the engine throttle can be closed to reduce flow through theengine while the engine is at rest.

At 518 engine oil pressure is also controlled while the engine is atrest. In one embodiment, an electrical pump can be controlled bycontroller 12, described in FIG. 2. The output of the electricallydriven oil pump can be adjusted in response to ambient conditions (e.g.,air temperature, air pressure, and the like) and in response to engineconditions (e.g., oil temperature).

Referring back to 512 of routine 500 in FIG. 5, if it is determined thatpush assist restart is not enabled, routine 500 moves to 520 where it isdetermined if shifting during engine off is enabled. As above, ifshifting during engine off is enabled, routine 500 moves to 524 where atransmission and torque converter shifting control is executed. Incontrast to the above scenario, however, in this case, the transmissionis shifted during engine off conditions in order to provide a smoothrestart where the transmission may provide an appropriate amount oftorque to the engine in order to quickly apply power and spin-up theengine from rest at restart. For example, the transmission may beshifted from neutral to a low gear to increase torque at restart.Similar to the previous scenario, once the shifting control is executed,routine 500 moves to 518 and the engine is shutdown and the routineends.

On the other hand, in either case, if it is determined at 514 or 520that shifting during engine off is not enabled, routine 500 proceeds to522. At 522 of routine 500, the transmission is shifted before shutdownto a gear appropriate for an expected/predetermined engine turn-onspeed. After the transmission is shifted, routine 500 moves to 518 wherethe engine is shutdown and the routine ends.

Referring back to 510 of routine 500 in FIG. 5, if it is determined thatthe engine is not on (e.g., the engine is off), routine 500 moves to 526where transmission and torque converter shifting control is executedbased on the vehicle speed, as described in the above examples. Notethat the transmission may be placed in neutral for engine starts whenthe starter is used to start the engine and when vehicle speed issubstantially zero.

Once the shifting control is executed at 526, routine 500 continues to528 where the engine restart routing of FIG. 6 is executed. The restartroutine will be described in greater detail below with reference to FIG.6.

As demonstrated by the flow chart of FIG. 5, routine 500 controls themanner in which the engine is shutdown. Depending on the functions thatare enabled by the controller, the transmission may shift to a desiredgear before the engine is shutdown or the transmission may shift to adesired gear while the engine is off.

Finally, the flow chart in FIG. 6 illustrates a control routine forsubsequently restarting the engine while the vehicle is traveling afterthe engine is shutdown or if the vehicle comes to a complete stop.Specifically, routine 600 decides whether or not to restart the enginein response to operating conditions. If an engine restart is desired,the engine may be restarted solely by an engine starter, by usingvehicle inertia (so long as vehicle speed is above a threshold), or by acombination of the two (so long as vehicle speed is above a threshold).The engine restart may be initiated by a throttle or torque demand, by achange in vehicle speed, by vehicle speed that is above or below athreshold, by a change in brake position, or by other conditions. Inresponse to conditions that initiate a restart, the engine may be setfor restart. For example, the engine throttle and cams may be positionedso that a desired engine torque is produced when combustion isreinitiated in the engine cylinders. In another example, fuel may beinjected directly into cylinders so that combustion can be initiated bya spark to shorten or improve the engine restart.

At 610 of routine 600, operating parameters are determined. For example,vehicle speed, change in brake position, a foot-off-brake event (e.g.,the operator releases the brake), change in vehicle speed, enginetemperature, engine after-treatment device temperature, and otherconditions. Further, combinations or sub-combinations of these and otherparameters may be determined if desired. Next, the routine proceeds to612 where it is determined whether or not to restart the engine. If anengine restart is desired the routine proceeds to 614. If not, theroutine exits.

Numerous embodiments are anticipated under which different conditionsare used to determine whether or not the engine is restarted. In oneembodiment, an engine restart is initiated when the vehicle speed isbelow a first threshold and above a second threshold. In thisembodiment, the first and second thresholds are used to define a vehiclespeed range in which the vehicle inertia may be used to at least assistengine restart. In another embodiment, the brake position (e.g., theposition of the vehicle brake pedal) and vehicle speed may be used todetermine when to restart the engine. For example, if the operator'sfoot remains on the brake, an engine at rest may stay at rest until thevehicle stops and the operator removes his or her foot from the brake.Further, the change in position of the brake pedal (e.g., the brakepedal is repositioned) may be used to initiate an engine start. Inanother embodiment, an engine restart may be initiated when the changein vehicle speed is below a threshold amount. For example, if theoperator's foot is off the brake and the vehicle is slowing because theroad grade is changing, the engine may be restarted. Further, differentsignals and combinations of signals may be used to determine when torestart the engine at 612.

At 614, routine 600 determines if the engine is rotating. If the engineis rotating, the routine proceeds to 626 where fuel injection, spark,and combustion are resumed. If the engine is not rotating the routineproceeds to 616.

At 616 engine controls are adjusted for restarting the engine. Inparticular, fuel timing, position of cams, spark timing(advance/retard), fuel injection location of start of injection, fuelinjection amount, fuel injection pressure, and throttle position may beadjusted to improve engine start. Further, combinations orsub-combinations of these and other parameters may be adjusted during orin anticipation of an engine start.

In one embodiment, as described above, fuel may be directly injected toa cylinder before engine rotation so as to assist in engine rotationwhen a spark is output to combust the injected fuel. Further, the fueltiming may be advanced or retarded relative to crankshaft angle at whichfuel was delivered to the engine prior to last engine stop.

In another embodiment, the throttle angle may be set so that acontrolled amount of air enters the cylinder during engine restart. Bycontrolling the amount of air entering the cylinder at start, enginetorque and emissions may be changed. Further, as mentioned above, theposition of the intake and/or exhaust cams may be adjusted during anengine start. By indexing the cams further control over cylinder aircharge and residuals may be provided. For example, in one embodiment,the cams may be adjusted to lower engine pumping work so that the enginecan be rotated by less torque. In this example, the cams can be furtheradjusted so that the amount of residuals is increased or decreased ascombustion is initiated.

If the vehicle is moving the engine control parameters mentioned abovemay be set in relation to vehicle speed. For example, cam timing,throttle position, fuel start of injection, fuel timing, and spark anglemay be adjusted such that the amount of torque generated by the engineat restart of the moving vehicle is at or slightly below the torquerequired to keep the vehicle moving at the present vehicle speed. In oneembodiment, a road load may be determined at a particular vehicle speed,and a desired engine torque may then be determined from the road load.As a result, the engine can be restarted such that the vehicle speeddoes not surge or decay from a threshold vehicle speed. In anotherembodiment, the engine may be restarted by adjusting one or more of thepreviously described engine control parameters to a first position ordemand at start, and then shortly after start or during engine run-up,to a second position or demand that is related to vehicle speed. Thus,operation of the engine can be controlled in relation to the vehicle sothat smooth transitions between operating the vehicle without the engineand operating the vehicle with the engine can occur.

In addition, throttle may be adjusted responsive to an operator demandat the time of engine restart. Thus, engine torque during start can beadjusted after road load torque is met. Routine 600 moves from 616 to618 after engine controls have been adjusted.

In one embodiment, when more push starting torque (e.g., more torque isprovided from the vehicle wheels to the engine by way of thetransmission) is provided by the transmission than torque provided bythe starter, the throttle may be set at a first position that is moreclosed than when the engine is started using less push starting torqueprovided by the transmission as compared to the starting torque providedby the starter. In this example, cam timing can be retarded, sparkretarded, and the fuel injection start of injection time can be retardedin order to further reduce engine torque during the engine restart.

In one embodiment, when less push starting torque is provided by thetransmission than torque provided by the starter, the throttle may beset at a second position that is more open than when the engine isstarted using more push starting torque provided by the transmission ascompared to the starting torque provided by the starter. In thisexample, cam timing can be advanced, spark advanced, and the fuelinjection start of injection time can be advanced in order to furtherreduce engine torque during the engine restart.

It should be noted that particular engine controls adjustments may bemade before or after it is determined whether the transmission orstarter or a combination thereof will be used to start the engine. Assuch, the order of execution describe by FIG. 6 may be varied.

At 618, the routine decides whether or not to use the starter to startor assist starting of the engine. Parameters determined at 610 may beevaluated in combinations and sub-combinations to determine whether ornot to start or assist the start of the engine using a starter.

In one example, if the vehicle speed is substantially zero, the starteris used to start the engine, but if the vehicle speed is above athreshold, the engine may be started by torque from the transmission orby the starter, or by a combination of the starter and the transmission.For example, the starter may be used to start the engine when thevehicle is moving and when vehicle speed is less than a first thresholdvalue. If the vehicle speed is greater than the first threshold value,but less than a second threshold value, the starter may be used incombination with the transmission to start the engine. And, if thevehicle speed is above the second threshold value, the transmission maybe the source of engine starting torque.

In another example, the vehicle speed may not go to substantially zerowithout starting the engine using transmission torque. In still anotherexample, the starter may be used to start the engine under allconditions while the transmission is used to start the engine, assistingthe starter, when vehicle speed is greater than a threshold. If astarter assisted engine start is desired, routine 600 proceeds to 620.If not, routine 600 proceeds to 624.

At 620, the routine engages the starter to start the engine. In oneembodiment, the starter pinion is engaged when the engine isrunning-down to substantially zero speed. The starter pinion remainsengaged until the engine is restarted. In this example, current torotate the starter is sent to the starter after starter assistance isrequested, otherwise the pinion can be withdrawn from the flywheelbefore transmission torque is applied to the engine. Current to rotatethe starter may be maintained until the engine reaches a thresholdspeed. Routine 600 then proceeds to 622.

At 622, routine 600 determines whether or not to assist the starter inthe engine start. As mentioned above, in one example, the transmissionmay assist the starter when vehicle speed is greater than a firstthreshold and less than a second threshold. If the transmission isassisting in the engine start, routine 600 proceeds to 624. If not, thestarter rotates the engine while spark and fuel are activated and theengine is started. Routine 600 exits when the engine is started.

At 624, the transmission is controlled to provide torque to start theengine. As mentioned above, the transmission may solely supplyrotational torque to the engine during an engine start, or thetransmission may supply a fraction of torque to start the engine.

In routine 600, the starter is engaged and current may be controlled torotate the starter motor before transmission applies torque to theengine. But in other embodiments, torque may be provided to start theengine by way of the transmission before the starter applies torque tothe engine. Thus, the order and timing of applying starter torque and/orengine torque to start the engine can be modified for differentconditions and objectives.

In an embodiment where the starter supplies torque to the engine beforethe transmission, the engine may begin to rotate before the transmissionclutch is applied. Under some conditions, the torque converter clutchmay be applied before the transmission forward clutch or gear clutch isapplied. Under other conditions, the torque converter clutch may beapplied after the transmission forward clutch or gear clutch is applied.When the transmission torque is applied with the starter torque, thetransmission clutches may be applied at an empirically determined ratethat is based on a table or function stored in memory.

In another embodiment, torque may be applied to start the engine solelyby the transmission. In this embodiment, a transmission clutch (e.g.,converter clutch, forward clutch, or gear clutch) is engaged accordingto a function that relates vehicle speed and current gear selected. Thefunction contains a clutch apply command profile that is used to outputa duty cycle or current command to regulate the force that is applied tothe clutch. Alternatively, the a function that is indexed by time sinceapplication of duty cycle, vehicle speed, and current gear selected maybe used to command the transmission clutches during a transmissionassisted engine start. In this way, the clutch apply profile allows thetransmission clutch to slip for a portion of the clutch apply period sothat there is not an abrupt change in torque that may be objectionableto the operator.

In another embodiment, a clutch apply profile based on vehicle speed andcurrent gear selected is modified in response to the transmission inputside shaft speed (e.g., the side of the transmission that mates to theengine) and the transmission output side shaft speed (e.g., the side ofthe transmission that mates to the driveline and tires). The input andoutput speeds are compared to determine an amount of slip. Thedetermined slip is then compared to a desired amount of slip and anerror term is then created. The error is added to the output of theclutch apply profile to correct the clutch apply command. When thetransmission input speed multiplied by the gear ratio substantiallymatches the transmission output speed, the clutch is engaged and theroutine proceeds from 624 to end.

Thus, in some embodiments, engine restart while the vehicle is travelingmay occur after the transmission has been shifted to a desired gearbased on the vehicle speed. In this manner, the transmission may beutilized to spin-up the engine quickly after the engine has beenshutdown in response to the above described braking conditions.

Note that threshold values described in FIG. 4-6 may be varied underdifferent operating conditions. For example, if the time since enginestart is short or if a temperature of an exhaust after treatment deviceis near a particular temperature, the engine speed threshold at whichDFSO is entered may be increased or decreased.

Further note that the example control and estimation routines includedherein can be used with various engine and/or vehicle systemconfigurations. The specific routines described herein may represent oneor more of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various acts, operations, or functions illustrated may be performed inthe sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments described herein,but is provided for ease of illustration and description. One or more ofthe illustrated acts or functions may be repeatedly performed dependingon the particular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A method for controlling an engine in a vehicle, the engine beingcoupled to a transmission, the method comprising: under a firstoperating condition, shutting-off the engine and spinning-down theengine to rest while the vehicle is traveling; and in response to asecond operating condition, restarting the engine by at least partiallyengaging the transmission to assist in spinning-up of the engine fromrest while the vehicle is traveling.
 2. The method of claim 1, whereinthe transmission is shifted to neutral before the engine is shut-off. 3.The method of claim 2, wherein a torque converter is engaged duringengine rest conditions.
 4. The method of claim 2, wherein a pump isdriven during at least engine rest conditions to maintain pressure of afluid.
 5. The method of claim 4, wherein the pump is driven by anelectric motor during engine rest conditions.
 6. The method of claim 1,wherein engaging the transmission to assist in spinning-up of the enginefrom rest includes applying a clutch to engage a gear in thetransmission.
 7. The method of claim 6, wherein the gear is selectedbased on a speed of the vehicle during or after the second operatingcondition.
 8. The method of claim 1, wherein the first operatingcondition includes application of a brake and vehicle speed below athreshold value.
 9. The method of claim 1, wherein the second operatingcondition includes a change in position of a brake pedal.
 10. A methodfor an engine in a vehicle, the engine being coupled to a transmission,the method comprising: in response to a first operating condition,shutting off a fuel supply to the engine; in response to a secondoperating condition, shutting off the engine and spinning-down theengine to rest; and during or before engine rest conditions, shifting agear of the transmission depending on a desired speed of the engine at athird operating condition.
 11. The method of claim 10, wherein shuttingoff the fuel supply to the engine includes deceleration fuel shut-off.12. The method of claim 10, wherein the vehicle is traveling duringengine rest conditions and the third operating condition is a change ina position of a brake pedal.
 13. The method of claim 12, furthercomprising a braking event that includes the first operating conditionand the second operating condition, and the second operating conditionfollows the first operating condition.
 14. The method of claim 12,further comprising a braking event including only the second operatingcondition when a vehicle speed is below a first threshold value when abrake is repositioned.
 15. The method of claim 14, wherein the secondoperating condition includes when a vehicle speed decreases below asecond threshold value during the first operating condition.
 16. Themethod of claim 15, wherein the second operating condition furtherincludes a difference in current engine speed and an idle speed of theengine less than a threshold amount.
 17. The method of claim 14, whereinthe braking event includes only the first operating condition when thevehicle speed does not decrease below the first threshold value before asubsequent foot-off-brake event.
 18. The method of claim 12, whereinduring engine rest conditions, a pump is driven to maintain pressure ofa fluid.
 19. The method of claim 12, wherein a desired speed of theengine at a subsequent change in brake pedal position is based on avehicle speed during the change in brake pedal position.
 20. A systemfor an engine in a vehicle, the system comprising: an automatictransmission having a plurality of gear ratios; the engine coupled tothe transmission via a torque converter; a control system configured to:shut-off a fuel supply to the engine responsive to a first operatingcondition; shut-off the engine and spin-down the engine to rest whilethe vehicle is traveling responsive to a second operating condition;during or after the second operating condition, shifting a gear of thetransmission depending on a desired speed of the engine at a subsequentthird operating condition; and in response to the third operatingcondition, restarting the engine by at least partially engaging thetransmission to assist in spinning-up of the engine from rest while thevehicle is traveling.